Tuesday, 2 June 2015

Have you ever watched a young child perform a delicate task with their hands and noticed how they stick out their tongue at the same time? A new study is the first to systematically investigate this behaviour in four-year-olds. This isn't just a cute quirk of childhood, the findings suggest, rather the behaviour fits the theory that spoken language originally evolved from gestures.

Gillian Forrester and Alina Rodriguez videoed fourteen 4-year-olds (8 boys), all right-handed, as they completed a number of tasks in their own homes. The tasks were designed to involve either very fine hand control (e.g. playing with miniature dolls or opening padlocks with keys), less fine control (e.g. a game of knock and tap, in which the child does the opposite to the researcher, be that knocking or tapping the table with their right hand), or no hand control (remembering a story).

The researchers studied the videos looking for how often the children stuck out their tongues during these different games, and whether they stuck them out towards the left or right side of their mouths.

All the children stuck out their tongues during the games and tasks, which supports past research with 5- to 8-year-olds that suggested this is a common behaviour. But crucially, the children stuck out their tongues more during some tasks than others, and most of all in the knock and tap game. This goes against expectations (the researchers thought the fine motor control games would provoke the most tongue protrusions) but Forrester and Rodriguez argue their surprise finding makes sense in terms of the evolutionary history of language. They explain the knock and tap game involves rapid turn-taking, hand gesturing and structure rules – what you could think of as "the foundational components of a communication system" or the rudiments of language.

This fits with another result, which is that most of the kids' tongue protrusions tended to be biased to the right, suggestive of control by the left brain hemisphere. The left side of the brain is the side that's more dominant for language in nearly all right-handers, so again we have a suggestion that children's gestural activities are accompanied by tongue protrusions because of the tongue and hands sharing a link with language and communication. The researchers think that adults (presumably excluding Miley Cyrus) suppress their own tongue protrusions because of the cultural connotations of sticking out your tongue.

Taken together with past research that's shown an overlap in the brain areas involved in speech and hand control, the researchers propose their new findings support the idea that the same communication system involves both the hand and the mouth, and that "hand and tongue actions possess a reciprocal relationship such that when structured sequences of hand actions are performed they are accompanied by spontaneous and synchronous tongue action".